Beavers and the Environment: Dams Help Remove Nitrogen From Estuaries and Restore Streams

Beaver dams are helping prevent harmful levels of nitrogen from reaching vulnerable estuaries in the Northeastern U.S., a new study revealed. Researchers from the University of Rhode Island discovered that ponds created from beaver dams slow the movement of water, which subsequently causes nitrogen build up. Along with organic matter build up this creates ideal conditions for scientists to adequately remove nitrogen, according to a news release.

With the increased use of agricultural fertilizers and urbanization, higher levels of nitrogen are seeping into local waters. Eventually, these toxic chemicals travel to estuaries where rivers meet the sea. Here, they stimulate the formation of algal blooms, which then – through processes of decomposition – remove necessary oxygen from the water. This is what scientists refer to as a "dead zone." Ultimately, this has led to increased fish mortality.

"What motivated us initially to study this process was that we were aware of the fact that beaver ponds were increasing across the Northeast," Arthur Gold, lead researcher from the University of Rhode Island, said in the release. "We observed in our other studies on nitrogen movement that when a beaver pond was upstream, it would confound our results."

Beavers have unique self-sharpened teeth that are strengthened with so much iron they appear orange. Their teeth are continuously growing so that they are never worn down from wood-chewing. These dam builders are also equipped with naturally oily, thick, waterproof skin; large, webbed feet; and paddle-shaped tails that help them maneuver through the water. Essentially, the animals go around chomping down trees with their big chainsaw-like teeth and carry the logs, twigs and branches back to add to their dams. As they build their water log cabins, they add mud and stones to fill in the gaps. Ultimately, their dams block off water in one section of the stream. This means the water backs up and forms a lake or a pond. (Scroll to read more...)

So, researchers set out to see if they could remove nitrogen from the concentrated ponds created by the beavers. To do this, they took sample cores of local soil and added nitrogen to them. This allowed them to simulate what happens on a much larger scale in the beavers' ponds. They discovered that bacteria in the organic matter of the soil cores were able to transform nitrogen, specifically a form called nitrate, into nitrogen gas. Ultimately this process allowed them to remove between five and 45 percent of the nitrogen from the water, according to the release. The amount they were able to remove depends greatly on the size of the pond and amount of nitrogen originally present.

"I think what was impressive to us was that the rates were so high," Gold explained. "They were high enough and beavers are becoming common enough, so that when we started to scale up we realized that the ponds can make a notable difference in the amount of nitrate that flows from our streams to our estuaries."

Julia Lazar, who conducted the work as part of her doctoral dissertation, added that their findings may change the way people think about beavers and their ponds. Especially since this is not the only way beavers have benefited environments with their dams. These animal construction workers have helped restore streams and replenish water supplies for local ecosystems and communities throughout the U.S. In fact, natural beaver dams have even helped boost threatened populations of stealhead salmon in Bridge Creek Oregon, according to the National Oceanic and Atmospheric Administration. When the beavers were able to plug the stream, they were essentially able to redirect the flow of water, which reconnected portions of the creek's channels, reduced erosion and helped restore the fish's natural habitat.

"Most of these beavers are in areas with smaller streams, not big rivers," Lazar explained in the release. "These smaller streams are usually the first to be developed, causing a decrease in beaver populations. So, it may be important to keep these areas from being developed so they can have effects on nitrogen levels downstream."